[Linux]Add/Delete sudoer/user on CentOS 8/REHL

when normal user want to use admin privilledge, error message:

"

user is not in the sudoers file.  This incident will be reported.

"

Add an existed user to sudoer: 

1. gain root command line access:
su
2. add an existed user user1 to sudoers:
useradd -G wheel user1
3. re-logon to apply new settings:
su user1
4. test sudo permissions:
sudo whoami
--if all went well, below commadns are 'root' output.

Add an non-exist user(newuser) to sudoer:
Step 1/2 the same
3. set password for new user:
passwd newuser

4. re-logon to apply new settings:
su user1
5. test sudo permissions:
sudo whoami
--if all went well, below commadns are 'root' output.

1. Take a note of the user and its username you wish to remove.
   
   You can list all system users by using the below cat command:

   # cat /etc/passwd
   

2. Use the userdel command to remove a user. In this example we will remove a user with username redhat-user. Please note the -r option instructs the userdel command to remove also user's home directory:

   # userdel -r redhat-user
   

3. Use the -f option to force the user removal in case the user is logged:

   # userdel -f -r redhat-user